With the growing concern over air pollution, it has become imperative that crankcase fumes, generated during the normal operation of an internal combustion engine, not be vented into the atmosphere. Numerous crankcase ventilation systems have been developed which recirculate such fumes into the fuel-air intake of an engine. However, with the the high efficiency engines of today a serious problem is created when the recirculated fumes contain an excessive quantity of oil vapors or mist. The delicate fuel-air balance can be upset and improper combustion can occur with all of its attendent problems. Prior art oil separators for crankcase fumes have been used with only limited success. The problem appears to reside in achieving an acceptable balance between a separator's capability of separating oil vapors and mist from the crankcase fumes and its capability to return the separated oil to the engine from the separator. Accordingly, it is a general object of this invention to produce an oil separator which effectively separates an acceptable amount of oil from the crankcase fumes and has an enhanced capability of effectively making the collected oil available to the engine crankcase.